1. Field of the Invention
The present invention relates to a marking method and apparatus which uses relief-plate printing.
2. Prior Art
In conventional marking devices, as shown in FIG. 4, a printing plate 50 is attached to a plate holder 51. The plate holder 51 is fixed to an oscillating lever 63 that is pivoted up and down via a cam 52. A spring 55 pulls the lever 53 downward so that the lever 53 pivots along the surface of the cam 52. Reference numeral 56 is a workpiece to be printed which is positioned and carried on a workpiece carrying table 57.
Since the plate holder 51 is driven by the cam 52, the distance the printing plate 50 is lowered is fixed. Accordingly, when the thickness of the workpiece 56 changes (due to the difference in the type of work performed), the distance between the printing plate 50 and the workpiece 56 must be adjusted by loosening the screw 54 and moving the plate holder 51 up and down.
The adjustment of the distance is performed as follows: after printing is performed, the condition of such a printing (i.e., the condition of contact of the printing plate 50 to workpiece 56) is examined, and then the height of the plate holder 51 is adjusted. Thus, considerable adjustment time is required. Since the condition of contact of the printing plate 50 with the printing surface of the workpiece varies depending upon the operator doing the adjustment job, uniform printing cannot be achieved.